Liquid crystal display types are divided into three kinds: a transmissive LCD which uses a backlight to provide illumination, a reflective LCD which reflects ambient light, and a transflective LCD which uses both a backlight and ambient light. A transmissive LCD is an ineffective light converter and only transmits about 3% to 8% of light from its backlight. Therefore transmissive LCDs require a backlight device having high brightness, leading to high power consumption. Reflective LCDs use ambient light for imaging, thus saving power consumption. However, although reflective LCDs can be used during the daytime, or in environments where external light exists, they cannot be used at night or under poor ambient lighting conditions.
Furthermore, the market demand for outdoor LCD applications is expanding. LCDs are needed for mobile navigator/video systems, PDAs, personal organizers, Tablet PCs, notebook computers, and Kiosk displays etc. Regular transmissive LCDs are of limited use for these applications because they are very difficult to read under strong ambient light. Therefore high brightness LCDs are sometimes used for outdoor applications. However, due to the high power backlight, high brightness LCDs suffer from high power consumption, excessive heat generation, increased dimensions, electrical circuit alterations, and shortened LCD lifetime.
In order to overcome the above drawbacks of transmissive and reflective LCDs, transflective LCDs have been developed to allow good legibility under any ambient light environment. In most transflective LCD displays each pixel is divided into reflective and transmissive sub-pixels. The transmissive sub-pixel does not have a reflector so it allows light from the backlight to pass through it and operates in transmission mode. Meanwhile, the reflective sub-pixel has a reflector for reflecting ambient light so that it can operate in reflective mode. Transflective LCDs operate well under all light conditions.
U.S. Pat. No. 7,015,997 teaches a method of producing a transflective liquid crystal display with a single cell gap, by partial switching of the pixels of approximately 45 degrees in the reflective pixel region of the single cell gap. This is achieved by applying fringing fields, generated by a discontinuous electrode, to the molecules in the reflective pixel region of the cell gap.
U.S. Pat. No. 6,989,878 discloses a transflective twisted nematic liquid crystal display with cell gap spacing in the transmission portion of the transflective LCD being approximately triple the cell gap spacing in the reflection portion of the transflective LCD.
U.S. Pat. No. 6,801,281 discloses a single cell gap transflective liquid crystal display with a slant reflector built on the path of the backlight. Light from the backlight thus traverses the reflective pixel portion twice and thereby follows a path similar to that of the ambient light.
US Patent Application 20060098114 disclose an array substrate for a transflective liquid crystal display device with a discontinuous transmissive electrode having a plurality of transmissive electrode portions and a reflector comprising a plurality of discontinuous reflector portions, the transmissive electrode portions and reflector portions are alternately disposed in order to optimise the light efficiency in both reflection and transmission modes.
US Patent Application 20050248697 discloses an LCD assembly comprising a backlight an liquid crystal panel and an optical element. The liquid crystal panel comprises a liquid crystal layer between two polarizers. The optical element comprises a liquid crystal layer between two glass substrates, but no polarizers. The optical element may be switched between a reflective mode in which it reflects light and a transmissive mode in which it transmits light. In this way the assembly may be switched between reflective and transmissive modes, but the pixels are not split into reflective and transmissive sub-pixels. Rather in the reflective mode each pixel acts in an entirely reflective manner and in the transmissive mode each pixel acts in an entirely transmissive manner. In this way it is hoped to maximize the brightness of the display.
US Patent Application 20050151902 disclose a transflective liquid crystal display with a single LC cell gap. A liquid crystal cell wall structure between the upper and lower substrates creates a first channel at reflective region and a second channel at transmissive region. The first and second channels may be filled with different liquid crystal materials. The first an second channels do not overly each other, so in general light passing through the display either passes through the first liquid crystal material (in the reflective region) or the second liquid crystal material (in the transmissive region) but not both.